Bodies that encounter fluid flow may cause vortex-induced vibration. More specifically, air or water flowing at sufficient velocity past a cylindrical, near-cylindrical or in general bluff body may create vortices downstream of the body. The vortices may detach periodically from the two sides of the body—a phenomenon called “vortex shedding.” Because the vortices have reduced pressure in their core, forces are created during vortex shedding that are directed toward the locations of the vortices. These forces can cause the body itself to oscillate, which is common for flexible antennas, or apply oscillatory loads to other parts of the vehicle, which is common for the skin or windows of the vehicle. If the frequency of the vortex shedding matches the resonance frequency of the body, the body may resonate at harmonic oscillations. Additionally, the pressure waves associated with the vortices may produce unwanted noise that may be observed inside the cabin.
In the field of aviation, certain parts of an aircraft such as probes, antennas and air inlets may be disposed outboard of the cabin and therefore exposed to a rapid air flow. A windshield wiper assembly, for example, may include a wiper arm that is positioned to engage a wiper blade with the exterior of a windshield. The wiper arm may include an arm portion that is disposed outboard of the cabin and therefore subject to the air flow generated around a nose of the aircraft during travel. On some aircraft and at certain airspeeds, noise may be observed in the cabin that may appear to be emanating from the vicinity of the wiper arms and therefore may be attributed to vortex shedding from these arms. In some instances the noise may be attenuated by reinstallation of the same wiper arm or replacement with a new wiper arm, however a reliable solution has not heretofore been proposed. A test flight with the wipers removed showed that the noise was eliminated, which confirmed the role of the wipers in creating the noise.